Shinwa Densetsu no Eiyuu no Isekaitan - Volume 10, Chapter 1 – Wriggling Darkness, Part 6

She is a top-class spy, a poison specialist, but also a young and cute girl with a sinister temperament. In spite of her sweet and innocent appearance, she can complete any tasks without the slightest hesitation. One day because of an incomplete black magic, she was sent into the body of a girl who was deemed as a good-for-nothing. What kind of change will she bring to this continent?

A Prince said with bitter hatred, “I thought she was weak and easily bullied, therefore I broke off the engagement. I really didn’t expect she is such a shrewd girl. I made an error of judgment.”

The Crown Prince deeply sighed, “She is such a sexy evildoer! Obviously, she has a frail and tender body, but I am not able to overwhelm her…”

Finally, an Emperor hit the nail on the head, “She is just a bit two-faced!”

She answered, “You’re just a big pervert!”

The Emperor carried her into the room and said, “You are predestined to be mine! A two-faced girl and a pervert are a perfect match, right?!”

- Description from Novelupdates

Project BIOHUMAN was supposed to be a quiet project that tested to see if they could create superhuman beings. The Creator, Dr. Vang Chang created the Numbers, ten individuals who took the BIOHUMAN serum and came out different.

Countries caught wind of this and demanded the Creator to disperse the serum to strengthen the humans. The BIOHUMAN serum was shot into the sky and dispersed all over the world. Little did anyone know, it changed Earth and everything living on it. Plants, animals and humans were genetically changed forever.

25 years later, the Creator's son, Lee Seng Chang is a high school student without any Biohuman powers. The serum had given him almost no Dark Matter and only increased his overall human abilities to a super-Biohuman level. Even with that, the power standing only made him seen as the weakest amongst everyone.

Picked on because of his powerless status, Lee Seng was left by all of his friends and labeled powerless. He desperately tries to keep going with a smile on his face. Lee Seng one day gets an option from a man with a Fox mask.

“Awaken your power but at a huge price.”

Lee Seng takes the deal and watches as the world he knew quickly changes and isn't what it seems. Put under the pressures of his Father's status and his new profound power and changes, Lee Seng battles the demons within him and the unknown coming for him.

What got summoned was the world’s strongest sociopath.

"Your granddaughter claims she likes girls while my grandson is rumoured to be bent so… don't you think they are a good match for each other?"